The present invention concerns a fuel injection valve having an integrated sparkplug.
A fuel injection valve having an integrated sparkplug for direct injection of fuel into the combustion chamber of an internal combustion engine and for igniting the fuel injected into the combustion chamber is discussed in from German Published Patent Application No. 196 38 025. With this fuel injection valve having an integrated sparkplug, a valve closing body that opens on the outside works together with a valve body to form a seal seat. The valve closing body is designed in one piece with a valve needle extending into the interior of the sleeve-shaped valve body. The valve needle is guided through the valve closing body on one end and through a guide ring provided at the inlet on the other end. The valve body can receive an electrical high voltage over a high-voltage cable and it has an ignition electrode on its spray end. The valve body is surrounded radially by a ceramic insulating body which is in turn surrounded by a metal housing body having another ignition electrode. The valve needle and the valve closing body, which is designed in one piece with the valve needle, are actuated in the opening direction by an armature working together with a solenoid. The armature acts by way of a tappet on an insulating spacer which is in contact with the guide ring of the valve needle.
One disadvantage of this design of a fuel injection valve having an integrated sparkplug is that the valve needle does not have a high-voltage insulating element. Therefore, the insulation is provided by the aforementioned spacer, which is connected to the valve needle only in a non-positive manner but not in a positive manner. Therefore, this design is suitable only for externally opening fuel injection valves. Since only an opening force can be transmitted via the spacer to the valve closing body but no closing force can be transmitted via the valve needle to the valve closing body, a valve closing spring must be integrated into the valve body to produce the closing force. It is believed that this leads to a relatively complicated design and thus to relatively high manufacturing and assembly costs.
Another fuel injection valve having an integrated sparkplug is discussed in European Published Patent Application No. 0 661 446. Again with this fuel injection valve having an integrated sparkplug, no insulating element is provided in the valve needle. Instead, the high voltage is supplied via the valve needle, which is insulated radially on the outside by complicated insulating bodies extending in the feed direction. With this unfavorable design, a total of four insulating bodies are necessary, leading to high manufacturing and assembly costs.
The fuel injection valve having an integrated sparkplug an exemplary embodiment of the present invention has the advantage that an insulating section which provides insulation in the axial direction is integrated into the valve needle, separating the two metal guide sections from one another. The magnetic needle is guided through the metal guide sections which may be made of hardened steel, for example, and therefore permit precision manufacturing and their surfaces have a low coefficient of friction. A first guide section is arranged on the spray end and may be designed in one piece with the valve closing body. The second metal guide section is arranged on the inlet end with regard to the insulating section arranged between the guide sections and is guided in the insulating body. The guide sections having the insulating section are also connected in a positive manner as well as in a non-positive manner, so that force can be transmitted via the valve needle in the opening direction as well as the closing direction. Therefore, it is not necessary to integrate a restoring spring inside the valve body. This yields a simple design which can be produced at a low manufacturing and assembly cost. The insulating body can be manufactured as an injection molded ceramic part at a low manufacturing cost. Since the insulating section is responsible only for the insulation and not for guidance of the valve needle, it is believed that no particularly high demands are made of the manufacturing accuracy and abrasion resistance of the insulating section.
The fuel injection valve an exemplary embodiment of the present invention having an integrated sparkplug has the advantage that the valve needle designed as a one-piece ceramic part with the valve closing body can be designed to be especially short, because no metal parts are used and the total length of the valve needle functions as an insulating path. Shortening the valve needle yields a definite reduction in weight, which in turn leads to relatively short switching times.
It is advantageous to design the insulating section of the valve needle as a ceramic sleeve body, because an especially low weight, and thus a short switching time, is obtained because of the material saved when the insulating section is designed as a sleeve body. The connection between the guide sections and the insulating section is preferably by way of connecting pins which engage in corresponding recesses. The connection can be accomplished by friction flow, gluing or even in part by shrink fit.
If the valve needle and the valve closing body are designed as a one-piece ceramic part, the valve closing body is preferably spherical or partially spherical in shape to prevent material from splintering out in the seat area.
The insulating body preferably has a recess at the side through which a high-voltage cable is guided to the valve body and is electrically connected to it. It is advantageous to fill the recess with a casting compound which provides electrical insulation, because this yields especially good protection of the welded or soldered junction of the high-voltage cable with the valve body. It may be especially advantageous for an electric burn-off resistor or an insulating film with high-voltage strength to be cast in the casting compound to improve insulation of the solder joint or weld.
One embodiment of the present invention is illustrated in simplified form in the drawing and explained in greater detail in the following description.